The invention relates to a locking apparatus, for example for household-device doors, having a locking member that can be moved between an open and a closed position by a bimetallic drive.
Bimetal-controlled locking apparatuses for household-device doors are generally known. In a lock for a washing-machine door, in particular, which is known from DE 37 09 660 C2, a bimetallic snap disk is provided as the drive for a stopper that blocks the manually-operated locking member in the locked position. This bimetallic snap disk assures, on the one hand, a rapid blockage of the lock by the stopper when heating occurs. After such a blockage, the heating current for the bimetal snap disk is cut off. As it cools, the disk returns to its open position. The bimetallic heating of the snap disk serves solely to move a stopper for a blocking member, not directly for the locking member.
The present object is to ensure, with simple means, that a locked door cannot be opened, even with an interruption or breakdown of voltage. This is especially important for household devices that operate at very high temperatures. In these cases, the locked state must be maintained until cooling to non-dangerous levels has occurred, even if the current supply fails.
In addition to the high safety requirements, a particular object is to produce the locking apparatus simply, and therefore inexpensively. It should be compact so as not to limit the freedom in the designing of the device. Finally, the apparatus should operate in an energy-saving and environmentally-friendly manner, e.g., quietly.
These objects are accomplished or facilitated by a locking apparatus which is characterized in that the locking movement and the unlocking movement are respectively driven by separate bimetal members over only a first segment of their movement path, thereby supplying energy to the energy store of a tipping over-center device until a dead-center position has been attained, the energy being re-released when the dead-center position of the tipping over-center device has been exceeded, and used as a movement drive for the remaining segment of the movement path, and stabilizing the locking member in its end position at the end of the respective movement path. The bimetallic drives directly control the locking and unlocking movements, and not only a stopper that blocks the mobility of the locking member in the closed position. Power consumption only occurs during the switching process, and then only for controlling the first component of the locking or unlocking movement until the dead-center position of the tipping over-center device has been exceeded. Afterward, the tipping over-center device assumes control of not only the second component, that is, the completion, of the displacement movement or switching process, but preferably also the cutoff of the electrical bimetal heating. The functional system is therefore currentless once the dead-center position of the tipping over-center device has been exceeded; the locking or unlocking position is nevertheless stable. Both the locking and unlocking movements are preferably controlled in this manner. The attained end statexe2x80x94that is, the locked and unlocked positionsxe2x80x94is stable. The entire system is bistable.
A further, special advantage lies in the structurally simple and, most importantly, compact construction that is attained particularly by a lowered positioning of the locking bar in comparison to the two bimetal members. Using a locking bar or a drive member that is inserted into or rests upon the moving ends of the two bimetal members permits an especially lowfriction drive of the locking bar, on which the bimetals act practically directly. The fact that the locking bar in the preferred embodiment is configured in two parts due to its position straddling a drive element that is disposed parallel to it and performs the same drive function has its basis in production and assembly considerations. The two parts could also be connected to one another to form a one-piece locking bar. This two-part embodiment offers a suspended retention and seating of the coupling-bridge drive member at the ends of the bimetals, without bearing forces that act on the locking bar acting on the coupling bridge, and thus the bimetals, thereby impairing the suspended seating of the coupling bridge, which is kept in contact with the bimetal ends by the energy store of the tipping over-center device.
Furthermore, the coupling bridge and the locking bar encapsulate the tipping over-center device between them, shielding it from the bimetal drive. All of the movements of the functional parts of the locking apparatus are completed in the longitudinal plane of the housing. This also facilitates an easy-to-assemble design.